Spring 源码(17)Spring Bean的创建过程(8)Bean的初始化

知识回顾

Bean的创建过程会经历getBeandoGetBeancreateBeandoCreateBean,然后Bean的创建又会经历实例化,属性填充,初始化。

在实例化createInstance时大致可以分为三种方式进行实例化:

  • 使用Supplier 进行实例化,通过BeanFactoryPostProcessorBeanDefinition进行修改,增加一个Supplier属性,放置一个lambda表达式用于创建对象
  • 使用factory-method进行实例化
    • 使用实例工厂实例化
    • 使用静态工厂实例化
  • 使用构造器反射进行实例化
    • 使用SmartInstantiationAwareBeanPostProcessor解析构造器,然后反射实例化
    • 使用无参构造器进行实例化

在属性填充populateBean时大致可以分为4个步骤:

  • 调用InstantiationAwareBeanPostProcessor接口的after方法修改Bean的信息
  • 自动装配,将解析的属性和属性值放入到pvs变量中
    • autowireByType自动装配
    • autowireByName自动装配
  • 执行通过CommonAnnotationBeanPostProcessorAtowiredAnnotationBeanPostProcessor解析的注解,然后注入到字段上
  • 对属性的值进行解析,解析pvs, 会涉及到参数转换,spel表达式解析,引用类型,String类型,List类型,Map类型,Set类型,Properties类型的解析,属性编辑器的解析等。

接下来解读初始化阶段

bean的初始化

bean的初始化initializeBean方法,直接上源码:

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {   if (System.getSecurityManager() != null) {     AccessController.doPrivileged((PrivilegedAction<Object>) () -> {       invokeAwareMethods(beanName, bean);       return null;     }, getAccessControlContext());   }   else {     // 执行Aware 方法     invokeAwareMethods(beanName, bean);   }    Object wrappedBean = bean;   if (mbd == null || !mbd.isSynthetic()) {     // 执行 BeanPostProcessor before 接口     wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);   }    try {     // 执行 init-method 方法     invokeInitMethods(beanName, wrappedBean, mbd);   }   catch (Throwable ex) {     throw new BeanCreationException(       (mbd != null ? mbd.getResourceDescription() : null),       beanName, "Invocation of init method failed", ex);   }   if (mbd == null || !mbd.isSynthetic()) {     // 执行BeanPostProcessor after 方法     wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);   }    return wrappedBean; } 

源码逻辑也很简单,大概就分成了4步:

  • 执行Aware接口的方法invokeAwareMethods
  • 执行BeanPostProcessor#postProcessBeforeInitialization
  • 执行初始化方法
  • 执行BeanPostProcessor#postProcessAfterInitialization

执行Aware接口的方法

点进去:

private void invokeAwareMethods(String beanName, Object bean) {   if (bean instanceof Aware) {     // 执行BeanNameAware     if (bean instanceof BeanNameAware) {       ((BeanNameAware) bean).setBeanName(beanName);     }     // 执行BeanClassLoaderAware     if (bean instanceof BeanClassLoaderAware) {       ClassLoader bcl = getBeanClassLoader();       if (bcl != null) {         ((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);       }     }     // 执行BeanFactoryAware     if (bean instanceof BeanFactoryAware) {       ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);     }   } } 

这里只执行了3个接口的方法,BeanNameAwareBeanClassLoaderAwreBeanFactoryAware,在Spring容器中不止这些Aware接口,这里为什么只执行了三个Aware接口?

Spring容器BeanFactory构造时,对这三个接口进行了忽略:

public AbstractAutowireCapableBeanFactory() {   super();   ignoreDependencyInterface(BeanNameAware.class);   ignoreDependencyInterface(BeanFactoryAware.class);   ignoreDependencyInterface(BeanClassLoaderAware.class); } 

所以这里只执行了这三个Aware接口,这里忽略,实际上就是不然这些属性通过自动装配设置属性值,而是通过Spring自己的回调进行设置值。

另外我们在开始的准备BeanFactory的时候又进行了忽略Aware接口:

beanFactory.ignoreDependencyInterface(EnvironmentAware.class); beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class); beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class); beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class); beanFactory.ignoreDependencyInterface(MessageSourceAware.class); beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);  

这6个接口在哪里执行的呢?在BeanFactory准备阶段注册了一个BeanPostProcessor的实现叫ApplicationContextAwareProcessor类,这个类的before方法中就进行了调用:

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {   if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||         bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||         bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){     return bean;   }   AccessControlContext acc = null;   if (System.getSecurityManager() != null) {     acc = this.applicationContext.getBeanFactory().getAccessControlContext();   }   if (acc != null) {     AccessController.doPrivileged((PrivilegedAction<Object>) () -> {       invokeAwareInterfaces(bean);       return null;     }, acc);   }   else {     // 执行Aware接口     invokeAwareInterfaces(bean);   }    return bean; }   private void invokeAwareInterfaces(Object bean) {   if (bean instanceof EnvironmentAware) {     ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());   }   if (bean instanceof EmbeddedValueResolverAware) {     ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);   }   if (bean instanceof ResourceLoaderAware) {     ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);   }   if (bean instanceof ApplicationEventPublisherAware) {     ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);   }   if (bean instanceof MessageSourceAware) {     ((MessageSourceAware) bean).setMessageSource(this.applicationContext);   }   if (bean instanceof ApplicationContextAware) {     ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);   } } 

为什么要分开处理呢?

个人认为主要是做了个区分而已,前面三个接口输入BeanFactory范畴,而这6个接口属于ApplicationContext范畴,只是进行了归类处理而已。

执行BPP的Before方法

代码比较简单,就是循环的执行了BPPbefore接口,这里在执行的时候,实现上也执行了在Bean进行merge的时候解析的@PostConstruct注解。

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {   LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());   try {     // 执行初始化方法     metadata.invokeInitMethods(bean, beanName);   }   catch (InvocationTargetException ex) {     throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());   }   catch (Throwable ex) {     throw new BeanCreationException(beanName, "Failed to invoke init method", ex);   }   return bean; } 

这个方法的实现类为InitDestroyAnnotationBeanPostProcessor

执行初始化方法

执行初始化方法的时候,会分为两步,一个是执行InitializingBeanafterPropertiesSet方法,另一个是执行自定义的init-method方法

protected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd)   throws Throwable {   // 判断当前Bean是否是实现了InitializingBean   boolean isInitializingBean = (bean instanceof InitializingBean);   if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {     if (logger.isTraceEnabled()) {       logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");     }     if (System.getSecurityManager() != null) {       try {         AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {           ((InitializingBean) bean).afterPropertiesSet();           return null;         }, getAccessControlContext());       }       catch (PrivilegedActionException pae) {         throw pae.getException();       }     }     else {       // 执行       ((InitializingBean) bean).afterPropertiesSet();     }   }    if (mbd != null && bean.getClass() != NullBean.class) {     String initMethodName = mbd.getInitMethodName();     if (StringUtils.hasLength(initMethodName) &&         !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&         !mbd.isExternallyManagedInitMethod(initMethodName)) {       // 执行自定义的初始化方法       invokeCustomInitMethod(beanName, bean, mbd);     }   } } 

执行BPP的after接口

BPP的after主要是用来实现AOP的,所以这里简单介绍下,循环执行after方法的调用。

源码:

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)   throws BeansException {    Object result = existingBean;   for (BeanPostProcessor processor : getBeanPostProcessors()) {     Object current = processor.postProcessAfterInitialization(result, beanName);     if (current == null) {       return result;     }     result = current;   }   return result; } 

源码比较简单,就循环执行了方法的调用。

初始化就解读完了,SpringBean的创建也基本讲完,最终创建出来的Bean对象就会放入到一级缓存singletonObjects中。

商匡云商
Logo
对比商品
  • 合计 (0)
对比
0
购物车